Integrate SockFuzzer as benchmark

I think [SockFuzzer](https://github.com/googleprojectzero/SockFuzzer) ([blog](https://googleprojectzero.blogspot.com/2021/04/designing-sockfuzzer-network-syscall.html)) is one of the most important libfuzzer targets out there.
We should integrate it as a benchmark.
A challenge here is support for non-libFuzzer based fuzzers. SockFuzzer uses libprotobuf-mutator (LPM).
I know AFL++ can use LPM but I'm sure this won't be trivial to get SockFuzzer's build system to work with AFL++.
As for non-AFL++/libFuzzer based targets, I assume they won't be able to fuzz SockFuzzer.